With the opening 2016 primary contest four weeks away, the billionaire businessman is spotlighting his plan to ban Muslims from entering the US - temporarily and with exceptions, he says - and to build a wall along the southern border.

Mr Trump's campaign says he plans to spend two million dollars (£1.36 million) a week on the ad, set to begin airing today across the first two states to cast votes in the Republican nominating contest.

Iowa hosts the nation's first presidential caucuses on February 1 and New Hampshire follows with the opening primary election on February 9.

Donald Trump's proposal has been condemned by Republicans and Democrats (Image: Mike Blake/Reuters)

The real estate magnate, who leads the Republican field nationally, is fighting for a good showing in the lead-off states against several rivals, particularly Senator Ted Cruz.

Mr Trump's proposal on Muslims has been condemned by Republicans and Democrats as un-American and counterproductive, yet the hardline approach to immigration has fuelled his popularity among the overwhelmingly white Republican primary electorate.

The new ad features dark images of the San Bernardino shooters, who were Muslims, and body bags.

"The politicians can pretend it's something else. But Donald Trump calls it radical Islamic terrorism. That's why he's calling for a temporary shutdown of Muslims entering the United States until we can figure out what's going on," a narrator says.

Video footage later in the ad shows people apparently streaming freely across a border as the narrator says Mr Trump will "stop illegal immigrants by building a wall on our southern border that Mexico will pay for".